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Subject: Re: [PATCH v3 2/3] arm64: implement update_fdt_pgprot()
To:     Hsin-Yi Wang <hsinyi@chromium.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
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        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Miles Chen <miles.chen@mediatek.com>,
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        Jun Yao <yaojun8558363@gmail.com>, Yu Zhao <yuzhao@google.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Laura Abbott <labbott@redhat.com>,
        Stephen Boyd <swboyd@chromium.org>,
        Kees Cook <keescook@chromium.org>
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From:   James Morse <james.morse@arm.com>
Message-ID: <5f598806-1c36-7c2a-0f47-da79ec7d28c6@arm.com>
Date:   Thu, 16 May 2019 18:34:16 +0100
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Hi!

On 16/05/2019 17:48, Hsin-Yi Wang wrote:
> On Thu, May 16, 2019 at 11:32 PM Rob Herring <robh+dt@kernel.org> wrote:
>> Doesn't kexec operate on a copy because it already does modifications.

It does!

> This patch is to assist "[PATCH v3 3/3] fdt: add support for rng-seed"
> (https://lkml.org/lkml/2019/5/16/257). I thought that by default
> second kernel would use original fdt, so I write new seed back to
> original fdt. Might be wrong.
> 
> ** "[PATCH v3 3/3] fdt: add support for rng-seed" is supposed to
> handle for adding new seed in kexec case, discussed in v2
> (https://lkml.org/lkml/2019/5/13/425)
> 
> By default (not considering user defines their own fdt), if second
> kernel uses copied fdt, when is it copied and can we modify that?

Regular kexec's user-space already updates the dtb for the cmdline and maybe the initrd.
For KASLR, it generates its own seed with getrandom():

https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/tree/kexec/arch/arm64/kexec-arm64.c#n483

If user-space can do it, user-space should do it!


Thanks,

James